EmperorSunshine is right. It's not a question of which way is up, its a question of whether your vision is in accord with that part of your brain that tells you how to move. When people are fitted with image-reversing glasses, eventually they say that the image has righted itself. That's something you could theoretically test for - does their brain rewire to invert the already-inverted image from the optic nerve, or does that part of their brain that tells them how to move rewire itself?

Rap wrote:This question is so interesting because the answer is not what you might expect at first glance. Your brain does not "flip" the image. As Darby said, it simply processes it. I think newborn babies haven't learned to process it yet. If you fitted a newborn with image-reversing glasses, they would learn to process it properly. Then, when they grew up and you had two adults, one with glasses, one without, you could never figure out which had the glasses and which did not by asking them questions, (except questions like "are you wearing reversing glasses"). I mean, any question you asked them about which way was up and down, you'd get the same answer. Ask them if their image is "reversed" and they would both say no, it looks fine. There is no "up" or "down" other than what you have learned. Their experience will be the same. If you took the glasses off the one person and put them on the other, then both would see things upside down.

Hi Rap. You make a very good point. Does our image actually flip? Does the brain actually turn the image like a single lens reflex, rather than a box brownie? I think it does. There are cases where a blow to the head can reverse the image temporarily, which suggest that when the brain is working properly it DOES flip the image. Yet none of the explanations given as to why it is easier to function with a flipped image hold water. There must be a proper explanation. What is it?here is an interesting thought. Perhap it's cultural? Nowadays we know that we are held onto a planet that is floating in space, by gravity. Therefore if the image was reversed it wouldn't interfere with our weltenschauung. Primitive man beleived the world was flat and that if you were to go to the edge of it you would fall off. a reversed image would possibly compromise this point of view. In other words if the image had remained reversed we would never have ended up believing what we do now. Our whole culture would have run along different lines. Just a thought.

No, I think the answer is subtle and hard to explain. Your brain does not flip the image, it simply deals with it. Your brain does not see the image and say "thats wrong, I must correct it". Your brain doesn't know that its "wrong". The subtle part is that there is no "right" or "wrong". Your brain simply deals with the image, and in so doing, you get a sense of up and down. Its only when you look at someone's retina and see that the image is reversed that an apparent problem occurs. If you were to program a robot with an eye and a hand, you wouldn't first reverse the image. You would simply write a program that dealt with the image and the hand. Its almost like saying "no, your brain doesn't reverse the image, it simply tells your hand to move the wrong way". But that assumes right and wrong, and so its not correct. Your brain is a bunch of neurons feeding it input. Your brain's sense of up and down is determined by that input, and how it has learned to deal with that input. It has no understanding beyond that of what is up and down, and doesn't need any, and, more subtly, none exists.

animartco wrote:Does our image actually flip? Does the brain actually turn the image like a single lens reflex, rather than a box brownie?

There is no "image." Your brain isn't like a television. It directly processes the signals coming in from your optic nerve - at no point does it try to reconstruct what your retina is seeing.

If you're interested in this, the vertebrate visual system is one of the best studied and best understood aspects of neuroscience. There are many great books that explain not only what we know about vision, but also how we know it.

Darby wrote:Almost everything your brain does in the optic area is process the almost-raw images.

Yes, obviously. Your brain starts with a bunch of signals on your optic nerve (which have only been minimally processed), but ends up with highly processed information. However, none of this actually requires reconstructing the complete image on the retina.

Just do a blind-spot test and you'll see that it reconstructs - and constructs.

Wouldn't this be evidence AGAINST your explanation? If your brain is making inferences about what's in your blindspot, that suggests it ISN'T reconstructing the actual retinal image.